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AI Servo, AF point selection question for close moving objects

ilzho
Super Contributor

Hello:

 

I just came back from the horse race track and looking through some of the photos, the camera/lens (of course not the photographer 🙂 ) couldn't get the horses in sharp focus when they were bunched together racing by.

 

I have a Rebel XSI (2008) and the manual stated to keep the automatic AF point selection (all 9 points) when shooting in AI servo.

 

I would like to know your thoughts?

 

I tried the center only AF point and it worked good as long as I kept it on the horse as it raced by 🙂 even in bunches.

 

Thanks,

David

 

 

16 REPLIES 16

diverhank
Respected Contributor

For cameras such as yours that have only 9 points, I think you should have only the center point.  Having all nine points will mean that the camera will choose a random one for you.  When you have a bunch of horses and you wish the lead horse to be in focus...the camera will most likely choose the one in the middle or at the end...

 

As you have seen, tracking moving objects with only one point is difficult.  Cameras that have more than 9 points will generally allow you to use the center point plus several more around the center to make tracking the target a bit easier.

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Diverhank's photos on Flickr

ilzho
Super Contributor

Thank you.

Yeah I knew better than to use all 9..... Sometimes it tracked the **bleep** railing, hahaha......

Just goes to show you it's not the equipment, it's the photographer 🙂

 

I'm going to buy a good camera as this is my brothers and he eventually wants it back.

cicopo
Esteemed Contributor

Depending on what the camera allows (Rebels likely don't offer this) use center point or expanded center point & put it on the horse that you specifically want as the main interest in the photo. IF the camera offered picking an expanded point other than the center area you might want to use the one opposite the centre point from the direction they are heading so the lead horse is the main focus but you have more horses in the frame behind it. When I frame an R/C model with the smoke on I want the plane on 1 side of the frame with the smoke trail going across to the other side rather than 1/2 the smoke trail because I had the plane in the center of the frame.

 

INGR5664.JPG 

"A skill is developed through constant practice with a passion to improve, not bought."

The correct technique is to use the center point first on the subject to acquire focus. Then, if the camera moves away from the center point one of the other points will pick it up and focus. If you don't have AF Point selected, I.e. only have center point, if the subject leaves the center point the camera will choose the next thing the center point sees. 

 

If if you move the camera to keep the center point on the subject then center point only is OK. 

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, MX472, LR Classic

ilzho
Super Contributor

Yes, I previously had the center point on and panned the horse/s and it seemed to work fine, then reading the manual (I'm a newbie still learning) I decided to use the AF automatic ponits... bad choice, haha.

Here's a bad example, but you get the idea.

Yes I was far away and I only have a 100mm prime lens, but here you see the brown railing in focus, the horses, no way. It's a throw away.

IMG_6529.jpg

For subjects like this, where subject is moving parallel to camera, I get better results with One Shot Continuous. No need for camera to refocus since distance isn't changing. 

 

AI Servo benefit is predictive focus based on subject motion changing distance between camera and subject. 

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, MX472, LR Classic

ilzho
Super Contributor

To be honest I have never used one shot continuous. I have always used AI servo, continuous (center AF point), usually.....

It's easier when the subjects are separated.

Not the best pic, overcast day.

100mm, f/6.3 1/1000, 200 iso. TV mode

 

IMG_6471.jpg

Nice shot. 

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, MX472, LR Classic

ilzho
Super Contributor

Thank you so much....

I have a greater appreciation for all of this....

It's not easy Smiley Happy